204 University of California Publications. [ ZooLoGy 
& Sexual differences in form of body, anterior antennae and 
fifth pair of feet. Abdomen with five segments, genital orifice 
on left side; the fourth segment and furea shortened. The 
right anterior antenna is a grasping organ and joints 19-21 and 
22-25 are fused. The fifth pair of feet (fig. 49c) consists of a 
common middle part and a right foot of four joints, a left of 
three, each uniramous. The right especially has the form of a 
claw, which, because of a process on the joint preceding the 
terminal, becomes an incomplete forceps. 
1. Acartia tonsa Dana. 
Acartia tonsa Dana, 1848, p. 26. 
Acartia tonsa Giesbrecht, 1892, pp. 508, 522; pl. 30, figs. 7, 24, 
34; pl. 43, figs. 6, 10; 1898, p. 154. 
a) 
; 
Fig. 49.—Acartia tonsu. (a) Female, dorsal, X45. (b) Abdomen of male, 
dorsal, X55. (c) Fifth foot of male X138. Dz., right foot. 
(d) Fifth foot of female 138. 
ex. 
b 
Rostral filaments present, last thoracic segment rounded 
laterally ; abdomen of male (fig. 495) with spines on the second 
segment; anal segment with lateral hairs. Anterior antennae of 
female without thorns, not reaching to the posterior border of 
6 ee, > ~<a te 
